How to make Markdown/HTML comment to Bitbucket Pull Request via API?

I'm using Bitbucket API (2.0) to submit comments to Pull Rrequests but I'm having a hard time figuring out how to send "styled" comments either using Markdown or HTML.

I've only managed to send comments in raw mode so far.

This is the documentation

https://developer.atlassian.com/bitbucket/api/2/reference/resource/repositories/%7Busername%7D/%7Brepo_slug%7D/pullrequests/%7Bpull_request_id%7D/comments#post

This is the code that sends raw messages:

BITBUCKET_API_ROOT="https://api.bitbucket.org/2.0"
BITBUCKET_STATUS_API="$BITBUCKET_API_ROOT/repositories/$BITBUCKET_NAMESPACE/$BITBUCKET_REPOSITORY/pullrequests/$PR_ID/comments"


MESSAGE="this is my message."

echo "Pushing comment to $BITBUCKET_STATUS_API..."
curl --request POST $BITBUCKET_STATUS_API \
--user $BITBUCKET_USERNAME:$BITBUCKET_ACCESS_TOKEN \
--header "Content-Type:application/json" \
--silent \
--data "{\"content\": { \"raw\": \"$MESSAGE\" }}"

Trying to specify markdown, this way:

--data "{\"content\": { \"raw\": \"$MESSAGE\", \"markup\": \"markdown\"  }}"

results in:

{"type": "error", "error": {"fields": {"content.markup": "extra keys not allowed"}, "message": "Bad request"}}

Trying other things, like specifying the html field also didn't help.